Played a game of AV with Brian. It looks like the dice negation mechanic is the way to go. We had really crappy rolls but even still, we managed to deal 1-2 damage. The system was really flexible. Cover and abilites altered to-hit, then defense and abilities negated dice.
3 "Luck" coins per player. Coins refresh every round. 6 rounds. When model dies, owner gets 1 permanent coin added to the pool. Only the active model can use coins. All coin abilities can only be used once per model, per activation.
1 coin = +1 die when attacking
1 coin = +2 def if attacked
3 coin = regain 1hp